The present invention relates to a composition comprising:
a compound comprising two or more olefinically unsaturated groups comprising at least one electron-withdrawing functionality linked to a carbon atom of the unsaturated bond;
a compound comprising at least two mercapto-functional groups; and
a catalyst.
Unsaturated groups, such as acryloyl groups, can react with active hydrogen-containing compounds. Such a reaction is believed to involve an addition of an anion derived from the nucleophilic, active hydrogen-containing compound, acting as a donor, to the activated unsaturated group, which serves as an acceptor. When these active hydrogen-containing compounds are Cxe2x80x94H compounds such as malonic ester or acetoacetate, the reaction is known as the Michael addition reaction. It is also known that SH-compounds may function as active hydrogen-containing compounds in a reaction mechanism which is similar to the Michael addition reaction. Hereinafter, such a reaction mechanism with SH-compounds is called a thio-Michael reaction.
A composition such as described in the opening paragraph, which is curable by such a thio-Michael reaction, is known from European patent application EP-A 0 160 824. Catalysts mentioned in this disclosure are quaternary ammonium compounds, tetramethyl guanidine, diaza-bicyclo-undecene, and diaza-bicyclo-nonene. Thio-Michael reactions catalysed by these strong bases are hard to control. Such reactions take place either much too fast or not at all, depending on the concentration of the used catalyst. Tertiary amines may be present but, according to this publication, are not reactive at ambient temperatures. Furthermore, the base-catalysed reaction may suffer from acid inhibition.
Carbon dioxide present in the air or an acidic substrate may severely retard or even stop cross-linking.
U.S. Pat. No. 2,759,913 discloses a copolymerisation process of unsaturated monomers with mercapto-functional compounds with a basic catalyst such as trimethyl benzyl ammonium hydroxide. As mentioned above, reactions with such a catalyst are hard to control.
British patent application GB-A 2,166,749 discloses a room temperature curable coating composition comprising an unsaturated polyester and a compound comprising at least three thiol groups and a catalyst which is a tertiary amine, such as triethyl amine. However, as can be seen from the Examples in GB-A 2,166,749, this reaction takes about 16 hours to cure at ambient temperatures. Faster reaction will only take place at high temperatures.
European patent application EP-A-0 284 374 discloses a polymerizable vinyl compound having a polythioether skeleton prepared from a compound comprising two or more olefinically unsaturated groups comprising at least one electron withdrawing functionality linked to a carbon atom of the unsaturated bond, a compound comprising at least two mercapto-functional groups, and a catalyst such as diethylamine. It is not disclosed that these reactant as such may be used in a coating or adhesive composition.
United States patent U.S. Pat. No. 5,840,823 discloses an adhesive composition comprising a compound comprising two or more olefinically unsaturated groups comprising at least one electron-withdrawing functionality linked to a carbon of the unsaturated bond, and a compound comprising a plurality of groups selected from thiol groups, primary amino groups or secondary amino groups. However, in U.S. Pat. No. 5,840,823 it is not taught nor suggested to use a compound with primary or secondary amino groups in combination with a compound comprising thiol groups.
The object of the invention is to provide a composition which overcomes the above-mentioned drawbacks.
The object of the invention is achieved with a composition of the type described in the opening paragraph comprising a catalyst comprising at least one, optionally blocked, NH-group.
Surprisingly, it has been found that although the prior art teaches that strong basic catalysts are needed, thio-Michael curable compositions comprising a catalyst according to the invention show rapid curing at ambient temperatures. This has the evident advantage that short production times are possible. Energy costs can be saved since curing takes place at ambient temperatures. Furthermore, in comparison with Michael and thio-Michael reactions catalysed by strong bases, the reaction time is much less dependent on the amount of catalyst This is advantageous for ease of formulation. It has also been found that the process can be carried out with low viscous oligomers. This has the advantage that compositions can be prepared which contain few if any solvents, but are still sprayable. The reactive groups involved in the curing reaction are much less toxic than most cross-linkable reactive groups in other adhesives or coating compositions, such as isocyanates. After curing, the applied layer is resistant to hydrolysis and degradation. Also, the thermal stability of the sulphide bond is high.
In the compound comprising two or more olefinically unsaturated groups, the olefinically unsaturated groups comprise at least one electron-withdrawing functionality linked to a carbon atom of the unsaturated bond. The olefinically unsaturated bond may be a double or a triple bond. Preferably, the olefinically unsaturated groups of the compound comprising two or more olefinically unsaturated groups have a structure according to the following formula I: 
wherein at least one of R1, R2, R3, and R4 comprises an electron-withdrawing functionality linked to a carbon atom of the unsaturated bond and at least one of R1, R2, R3, and R4 is linked to a polyvalent group comprising at least two valencies.
Examples of the electron-withdrawing functionality include carbonyl, carboxyl, ester, thiocarbonyl, thiocarboxyl, thioesters, sulfoxide, sulfonyl, sulfo, phosphate, phosphite, phosphonite, phosphinite, nitro, nitrile, and amide.
In the case of R1, R2, R3, and/or R4 being monovalent, the electron-withdrawing functionality may be attached to a hydrogen atom, linear or branched alkyl, cycloalkyl, alkenyl, cyclo-alkenyl, alkynyl, cyclo-alkynyl, and aryl which may optionally be substituted with various other functionalities, such as carboxylic acid or hydroxide. If they do not comprise an electron-withdrawing functionality, R1, R2, R3, and/or R4 may be independently selected from a hydrogen atom, linear or branched alkyl, cycloalkyl, alkenyl, cyclo-alkenyl, alkynyl, cyclo-alkynyl, and aryl which may optionally be substituted with various functionalities, such as carboxylic acid or hydroxide. When at least one of R1, R2, R3, and R4 is linked to a polyvalent group and it is not an electron-withdrawing functionality, it may be a simple bond. The polyvalent group links at least two groups according to formula I. The polyvalent group may be selected from a simple bond, substituted or unsubstituted alkylene, cycloalkylene, alkenylene, cycloalkenylene, alkynylene, cycloalkynylene, arylene, or combinations thereof. The polyvalent group may optionally comprise hetero atoms such as xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94Sixe2x80x94, and xe2x80x94Pxe2x80x94, and groups such as amide, urea, and ester groups.
Preferably, the group according to formula I is derived from an unsaturated carboxylic acid comprising 2 to 10, preferably 3 to 6, carbon atoms. The carboxylic acid may be mono- or polyunsaturated and may be a monocarboxylic or polycarboxylic acid. Examples of suitable monocarboxylic acids are acrylic acid, methacrylic acid, cinnamic acid, propargylic acid, and dehydrolevulinic acid. Examples of suitable polycarboxylic acids are citraconic acid, maleic acid, itaconic acid, or the anhydrides thereof, and mesaconic acid and fumaric acid. Also monoesters of mono- and polycarboxylic acids and diesters of polycarboxylic acids may be used such as acrylic acid esters, maleic acid mononitrile-monoesters, diethyl maleate, cyanoacrylic acid esters, and alkylidene malonic acid esters as disclosed in WO 98/41561. Acrylic acid or its ester, maleic acid, its ester or anhydride are preferred.
When the group according to formula I is derived from acrylic acid or its ester, a suitable example of a compound comprising two or more olefinically unsaturated groups includes trimethylol propane triacrylate.
When the group according to formula I is derived from maleic acid, ester(s) or anhydride, suitable examples of compounds comprising two or more olefinically unsaturated groups include polyesters of diethyl maleate with diols, such as 1,5-pentane diol, 1,3-propane diol and/or 2-butyl-2-ethyl propane diol, optionally reacted with polyisocyanates; the reaction product of an epoxy-functional compound, such as Cardura(copyright) E10 (an aliphatic epoxy compound available from Shell Chemical Company), and isobutyl monomaleate, further reacted with the trimer of isophorone diisocyanate, e.g., Vestanat(copyright) T 1890 E, available from Hxc3xcls; and the reaction product of maleic anhydride, dipentaerythritol, and butanol.
Alternatively, the group according to formula I may be derived from unsaturated aldehyde.
Finally, the compound comprising two or more olefinically unsaturated groups comprising at least one electron-withdrawing functionality linked to a carbon atom of the unsaturated bond may be an unsaturated ketone, such as divinyl ketone or dibenzal acetone.
The compound comprising at least two mercapto-functional groups may be prepared by direct esterification of a mercapto-functional organic acid with a polyol. Examples of mercapto-functional organic acids include 3-mercaptopropionic acid, 2-mercaptopropionic acid, thio-salicylic acid, mercaptosuccinic acid, mercaptoacetic acid, or cysteine. Examples of compounds prepared according to such a method include pentaerythritol tetrakis (3-mercaptopropionate), pentaerythritol tetrakis (2-mercaptoacetate), trimethylol propane tris (3-mercaptopropionate), trimethylol propane tris (2-mercaptopropionate), and trimethylol propane tris (2-mercaptoacetate). A further example of a compound prepared according to such a method consists of a hyperbranched polyol core based on a starter polyol, e.g. trimethylol propane, and dimethylol propionic acid. This polyol is subsequently esterified with 3-mercaptopropionic acid and isononanoic acid. These methods are described in European patent application EP-A 0 448 224 and international patent application WO 93/17060. Another example of a compound comprising at least two mercapto-functional groups is a mercaptane functional polyurethane resin. In a first step, an isocyanate functional polyurethane is prepared from diols, diisocyanates, and building blocks containing groups which facilitate the stabilization of the resin in an aqueous dispersion. Such groups are for example polyethylene oxide derivatives, sodium sulfonate groups, and other ionic stabilizing groups. In a second step, the isocyanate functional polyurethane is reacted with di-, tri-, or tetra functional thiols, such as trimethylol propane trimercapto propionate and pentaerythritol tetramercapto propionate. The equivalent ratio of thiol groups to isocyanate groups in this step is between 2-5:1. Such a resin is suitable for waterbome coating composition.
Alternatively, the compound comprising at least two mercapto-functional groups may for example have a structure according to the following formula: T[(C3H6O)nCH2CHOHCH2SH]3, with T being a triol such as trimethylolpropane or glycerol. An example of such a compound is commercially available from Henkel under the trademark Henkel Capcure(copyright) 3/800.
Other syntheses to prepare compounds comprising at least two mercapto-functional groups involve:
the reaction of an aryl or alkyl halide with NaHS to introduce a pendant mercapto group into the alkyl and aryl compounds, respectively;
the reaction of a Grignard reagent with sulphur to introduce a pendant mercapto group into the structure;
the reaction of a polymercaptan with a polyolefin according to a nucleophilic reaction, such as a Michael addition reaction, an electrophilic reaction or a radical reaction;
the reduction of disulphides; and
other routes, as mentioned in Advanced Organic Chemistry by Jerry March, 4th edition, 1992, page 1298.
It is preferred that the mercapto-functional groups and the olefinically unsaturated groups are present in the composition in an equivalent ratio between 1:2 and 2:1, preferably about 1:1.
In an alternative embodiment of the present invention, the compound comprising two or more olefinically unsaturated groups comprising at least one electron-withdrawing functionality linked to a carbon atom of the unsaturated bond and the compound comprising at least two mercapto-functional groups may be one and the same compound. This embodiment results in a self-cross-linkable composition in the presence of a catalyst comprising at least one, optionally blocked, NH-group.
The composition of the present invention comprises a catalyst comprising at least one NH-group which may optionally be blocked. Catalysts comprising at least one NH-group are for example primary and secondary amines. Catalysts comprising at least one blocked NH-group are for example aldimines, ketimines, enamines, and oxazolidines. Also included are catalysts wherein a NH-group originates by daylight or UV radiation.
Examples of primary amines include isophorone diamine, butyl amine, n-octyl amine, n-nonyl amine, N,N-diethylamine-propyl-3-amine, 4-(aminomethyl)-1,8-octane diamine, aniline, methoxy aniline, carboxy ethyl aniline, phenylene diamine, and mixtures thereof. Also included are polyoxyalkylene amines, such as polyoxy ethylene/polyoxy propylene mono-, di, or triamines. These are available from Huntsman under the tradename Jeffamine(copyright), such as Jeffamine(copyright) T-403.
A suitable secondary amine is for instance di-octyl amine.
Other suitable catalysts are ketimines, i.e. the condensation products of primary amino groups with ketones, or aldimines, i.e. the condensation products of primary amino groups with aldehydes. In these condensation reactions, groups with the following formula are formed: 
wherein R5 is an alkyl group, a cyclic group, or an aromatic group, and R6 is hydrogen in the case of an aldimine or an alkyl group, a cyclic group, or an aromatic group in the case of a ketimine. Preferably, R5 and/or R6 are alkyl groups. More preferably, R5 and/or R6 are alkyl groups comprising 1-10 carbon atoms.
Examples of aldimines include the condensation products of monofunctional amines like n-octyl- or n-nonyl amine and polyfunctional amines like isophorone diamine with acetaldehyde, propionaldehyde, isobutyraldehyde, n-octyl aldehyde, 2-ethylhexyl aldehyde, or n-nonyl aldehyde. A commercial product is for example Vestamine(copyright) A139, isophorone bisisobutyraldimine, ex Hxc3xcls. Also aromatic aldehydes and dialdehydes and heterocyclic aldehydes and dialdehydes and mixtures thereof may be used. Examples of aromatic aldehydes include 4-acetamidobenzaldehyde, anthracene-9-carboxaldehyde, 3-benzyloxybenzaldehyde, 4-benzyloxybenzaldehyde, 3-benzyloxy-4-methoxybenzaldehyde, 3,5-bis(trifluoromethyl) benzaldehyde, 3-bromo-4-methoxybenzaldehyde, 5-bromo-2-methoxybenzaldehyde, 2-bromobenzaldehyde, 3-bromobenzaldehyde, 4-bromobenzaldehyde, xcex1-bromocinnamaldehyde, 3-bromo-4-fluorobenzaldehyde, 4-bromo-2-fluorobenzaldehyde, 5-bromo-2-fluorobenzaldehyde, 5-bromo-2-hydroxybenzaldehyde, 2-chlorobenzaldehyde, 3-chlorobenzaldehyde, 4-chlorobenzaldehyde, and other halogen substituted aromatic aldehydes, 4-butoxybenzaldehyde, 2,3-dihydroxybenzaldehyde and other isomers, 2,3-dimethoxybenzaldehyde and other isomers, 3,4-dimethoxy-6-nitrobenzaldehyde, 4-dimethylaminobenzaldehyde, 2,5-dimethyl-p-anisaldehyde, 2,4-dinitrobenzaldehyde, 4-phenoxybenzaldehyde, 3-phenoxybenzaldehyde, 4-phenylbenzaldehyde, p-tolualdehyde, o-tolualdehyde, and m-tolualdehyde, 2,4,6-trimethylbenzaldehyde and other alkyl substituted benzaldehydes. Examples of aromatic dialdehydes include 1,3-benzenedialdehyde and terephthalaldehyde. Examples of heterocyclic aldehydes include thiophene-2-carboxaldehyde, thiophene-3-carboxaldehyde, 5-acetoxymethyl-2-furaldehyde, 4-bromo-2-thiophenecarboxaldehyde, 3,5-dimethyl-1-phenylpyrazole-4-carboxaldehyde, 3-phenyl-1h-pyrazole-4-carboxaldehyde, picolinaldehyde, 4-pyridinecarboxaldehyde, 3-pyridinecarboxaldehyde, and 4-quinolinecarboxaldehyde. An example of a heterocyclic dialdehyde includes 2,5-thiophenedicarboxaldehyde.
Suitable ketimines are the condensation products of mono- and polyfunctional amines with for instance acetone, methylethyl ketone, methylisobutyl ketone, methylisoamyl ketone, ethylamyl ketone, cyclohexanone, acetophenone, hydroxyacetophenone, or acetyl biphenyl. One example is the reaction product of 3 moles of ethyl amyl ketone and 4-(aminomethyl)-1,8-octane diamine.
An example of a suitable oxazolidine is Incozol(copyright) LV, available from Industrial Copolymers Ltd., i.e. the reaction product of 1 mole of diallyl carbonate and 2 moles of an oxazolidine produced from diethanolamine and isobutyraldehyde.
An example of a suitable enamine is 1-pyrrolidino-1-cyclohexene.
Catalysts wherein an NH-group originates by UV radiation are disclosed by J. F. Cameron et al., J. Org. Chem., 1990, 55, pp. 5919-5922. Examples of catalysts wherein an NH-group originates by UV radiation include N-[[1-(3,5-dimethoxyphenyl)-1-methyl-ethoxy]carbonyl]cyclohexylamine, N,Nxe2x80x2-bis[[1-(3,5-dimethoxyphenyl)-1-methylethoxy]carbonyl]hexane-1,6-diamine, N-[[1-(3,5-dimethoxyphenyl)-1-methylethoxy]carbonyl]piperidine, [[1-(3,5-dimethoxyphenyl)-1-methylethoxy]carbonyl]amine, [[(2,6-dinitrobenzyl)oxy]carbonyl]cyclohexyl amine, 4,4xe2x80x2-[bis[[2-nitrobenzyl)oxy]carbonyl]trimethylene]dipiperidine, 3,3xe2x80x2,5,5xe2x80x2-tetramethoxybenzoin cyclohexyl carbamate, and mixtures thereof.
The NH-functional catalysts, optionally blocked, can be used alone, as mixtures of catalysts of the same nature, or as mixtures of catalysts of a different nature. In particular, if the composition according to the invention is used as a primer, it is preferred to use a mixture of aldimines and ketimines as a catalyst. A mixing weight ratio of 0,1-10:1, preferably 2-6:1, can be used. It has been found that this results in a better adhesion to the substrate.
Since the reaction time is only dependent on the amount of catalyst to a small extent, high concentrations of catalyst can be used without making the reaction uncontrollable. It has been found that the sensitivity of a base coat or top coat to an acidic substrate or primer, and hence the curing time, is lower when higher concentrations of catalysts according to the invention are used. This sensitivity is believed to be reduced even more if tertiary amines are added to the top coat or base coat composition, since they are believed to adhere to the used acidic primer or acidic substrate and to neutralise its acidity. The full amount of catalyst is then used to catalyse the reaction. A suitable tertiary amine is N,N-dimethyl-ethanol-amine.
Preferably, the catalyst is used in an amount of 0,01-10 eq. % nitrogen groups, based on the total of unsaturated and thiol groups. An amount of 0,1-6 eq. % is more preferred.
The composition according to the present invention may be a water-bome composition, a solvent-bome composition or a solvent-free composition. Since the composition may be composed of low viscous oligomers, it is especially suitable for use as a high-solids coating or a solvent-free coating. Preferably, the theoretical volatile organic content (VOC) of the composition is less than 450 g/l, more preferably less than 350 g/l, most preferably less than 250 g/l.
In order to further reduce the volatile organic content, reactive diluents may be used, such as diethyl maleate, methoxypropyl citraconimide, diethylbenzylidene malonate, an xcex1,xcex2-unsaturated aldehyde, e.g., cinnamaldehyde or citral, and monothiol functional compounds, such as dodecyl mercaptane and mercapto functional silanes, such as xcex3-mercapto-propyl-trimethoxysilane. The mercapto-functional groups and the olefinically unsaturated groups of the reactive diluents are also taken into account with regard to the above-mentioned equivalent ratio.
The present compositions are of particular interest in coating compositions or adhesives. Preferably, a two-pack composition is used. Preferably, the first component of the two-pack coating or adhesive comprises the compound comprising two or more olefinically unsaturated groups as well as the compound comprising at least two mercapto-functional groups, while the second component of the composition comprises a small amount of a catalyst solution. However, if so desired, the second component may comprise, next to the catalyst, a part or the total amount of either the compound comprising olefinically unsaturated groups or the compound comprising mercapto-functional groups.
The formulations may contain pigments, effect pigments, such as aluminium parts, UV absorbers, adhesion promoters, such as epoxy silane, HALS-type stabilizers, flow additives or other additives.
The composition according to the present invention can be applied by conventional methods, including spraying, brushing, roller coating or dipping. However, the composition of the present invention is particularly suitable for application by an external mixing apparatus, one wherein a liquid composition comprising:
a compound comprising two or more olefinically unsaturated groups comprising at least one electron-withdrawing functionality linked to a carbon atom of the unsaturated group, and
a compound comprising at least two mercapto-functional groups,
is sprayed via a spray nozzle, with a small amount of a liquid catalyst composition comprising at least one catalyst comprising at least one, optionally blocked, NH group, being injected into the spray of the sprayed composition.
Such an apparatus is described, for example, in WO 98/41316. Due to the very effective use of the catalysts, the compositions according to the present invention have very short curing times, which makes this method specifically suitable for these compositions.
The composition according to the invention can be used on various substrates, in particular wood, plastics, and metal substrates such as aluminium, steel, or galvanised steel, for industrial applications of any kind. The composition can be used for instance as an adhesive or as a coating, e.g., as a pufty, primer, filler, base coat, top coat or clear coat. The composition is particularly advantageous for use as a coating for car repair, since it is easily sprayable and can be applied at ambient temperatures. Generally in car repair, several layers need to be applied, such as a primer, a base coat, and a clear coat. Because of the short drying times, a next layer can be applied within a short time from applying a first layer.